MECHANICAL BEHAVIOUR OF ANISOTROPIC FOLIATED ROCKS: IMPLICATIONS FOR TUNNEL STABILITY AND DESIGN
DOI:
https://doi.org/10.55197/qjoest.v6i2.225Keywords:
rock anisotropy, foliated metamorphic rocks, triaxial compression test, tunnel stabilityAbstract
Understanding the mechanical behavior of anisotropic rocks is critical for the design and stability of underground structures, particularly in tunneling and deep excavation projects. This study investigates the effects of anisotropy on the strength, deformation, and failure mechanisms of foliated metamorphic rocks such as phyllite, schist, and gneiss using a combination of laboratory techniques, including triaxial compression tests, Unconfined Compressive Strength (UCS) tests, point load tests, and petrographic analysis. The results reveal a strong dependency of rock strength on bedding orientation. At 0° and 90° to foliation, rocks exhibited higher compressive strength, whereas at intermediate angles (particularly β=30°–45°), strength significantly decreased and failure became more pronounced. Triaxial testing showed that the influence of confining pressure was more effective at lower bedding angles, diminishing at steeper ones, indicating dominant anisotropic behavior. Petrographic analysis confirmed that mineral composition, particularly the presence of mica, along with microcracks and voids, plays a substantial role in weakening rock structure at certain orientations. Point load tests supported UCS findings and offered a practical means of estimating strength anisotropy. Crack propagation patterns also varied with loading angles, with brittle failure dominating at higher angles and shear failure observed along foliation planes at lower angles. This study underscores the necessity of accounting for anisotropy in geomechanical modeling and engineering design to ensure the structural integrity of subsurface constructions.
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